Method for manufacturing plastic bags



Oct. 25, 1966 M. GENNERICH ETAL METHOD FOR MANUFACTURING PLASTIC BAGS 4 SheetsSheet 1 Original Filed April 8, 1963 lnvenlars: Max GENNERICH, Kurt ROCHLA and KwI-Hemz TRAUTMANN Oct. 25, 1966 M. GENNERICH ETAL METHOD FOR MANUFACTURING PLASTIC BAGS 4 Sheets-Sheet 2 Original Filed April 8, 1963 Fig. 15

Fig. 14

2 An N M 0 {RM n w evwA. V n T Y1 Z 6 .m0m E W m A O 3 M 0 M Oct. 25, 1966 M. GENNERICH ETAL 3,28 ,705

METHOD FOR MANUFACTURING PLASTIC BAGS Original Filed April 8, 1963 4 Sheets-Sheet 5 Inventors:

Max GENNERICH, Kurt ROCHLA omd Kar -Hemz TRAUTMANN fheir Affor-ney 1966 M. GENNERICH ETAL 3,280,705

METHOD FOR MANUFACTURING PLASTIC BAGS 4 Sheets-Sheet 4 Original Filed April 8, 1963 u 9 In 1d 9 6 M m m ll 2 vlw 5 w n 0 OJ. 5 m F HUHHH l In ven tors:

M m A M T .T. U UA. KIR fi m K n M W e m T r a m a n MGIMJ United States Patent Claims. (in. 93-35 This application is a division of application Serial No. 271,162, filed April 8, 1963, now Patent No. 3,235,169 issued February 15, 1966.

This invention relates to the making of a plastic valve bag, which in the filled state assumes the form of a parallelepiped, as well as to a method and means for its manufacture.

A valve bag made of weldable material comprising gussets and ends each closed by a weld has already been disclosed. The filling valve of this bag is formed by folding in one corner, as has been customary for a long time in gusseted bags of paper which are sewn or glued at the ends. In the known valve bag of weldable material, the folded in part forming the valve opening, whichin a manner known from paper bag manufacturecan be extended and provided with a valve insert and/ or a valve extension, is welded at its upper edge together with the closing weld of the bag. This construction has the disadvantage that the valve tube thus formed, when the bag is filled and has parallelepipedic form, hangs down in a pear shape into the inside of the bag from the weld located in the middle of the respective side of the parallelepiped and under the effect of the contents of the bag cannot be brought into a perfect and reliable closure position. As soon as the contents on a change in the bag position, no longer press firmly against the valve tube, the latter opens and no longer performs a sealing function. In this state dirt and moisture can penetrate the bag from outside and on tilting of the bag, the contents may come out of it. In particular, owing to the great deformability of plastic material in contradistinction to paper, the valve is undesirably forced out of the valve opening by the contents.

The inventors have set themselves the problem of remedying this state of affairs and propose for this purpose a plastic valve bag with gussets, ends each closed by a weld and a filling valve formed by a folded in bag corner and a welded in extension or insert strip, which is characterized by the feature that the folded in and extended part forming the valve channel is secured to the bag walls along the edges of the parallelepiped wall (formed on filling) running parallel with the valve channel, by a weld on each side. As a result, when the parallelepipedic form is being assumed on filling of the bag, the valve tube is pulled out and flattened, so that regardess of the position of the bag, it assumes a closing position and reliably prevents discharge from inside and penetration from outside. By fixing the valve on the bag walls, inverting of the valve by the contents is rendered impossible.

A further inventive proposal consists in that use is made of a valve extension strip that does not reach as far as the closing weld of the bag, but has only substantially the width of the base plus twice the width of the weld. In contradistinction to the known embodiment, this improves the valve whilst at the same time saving material.

A substantial part of the invention is constituted by the method of manufacturing the bag defined above. The inventors have set themselves the problem of evolving a method of manufacture, which can be carried out mechanically. In the pertinent art a method of manufacture which can be carried out mechanically has not yet been disclosed for the above mentioned known plastic valve bag.

Finally the invention relates to parts of a device for carrying the method into effect.

Various embodiments of the plastic valve bag according to the invention as well as the method and parts of the device for its manufacture are described in more detail hereunder with reference to the accompanying drawings, in which:

FIGURE 1 shows an embodiment of the plastic valve bag according to the invention in a preliminary stage of its manufacture.

FIGURE 2 is a section along the line A-B of FIG- URE 1.

FIGURES 3 to 6 show modified embodiments of the plastic valve bag according to the invention in the same stage of manufacture as in FIGURE 1.

FIGURE 7 is a section substantially along the line C-D of FIGURE 8 through the plastic valve bag according to FIGURE 1 in the next stage of its manufacture.

FIGURE 8 shows the flat finished plastic valve bag according to FIGURES 1, 2 and 7.

FIGURE 9 is a section along the line C-D of FIG- URE 8 with the bag walls slightly spread out.

FIGURE 10 shows the fiat finished plastic valve bag in the embodiment according to FIGURE 5.

FIGURE 11 shows the valve corner of the finished flat plastic bag in the embodiment according to FIG- URE 6.

FIGURE 12 shows the plastic valve bag according to FIGURES 1, 2, 7 and 8 in the filled parallelepipedic state.

FIGURE 13 shows a further embodiment of the plastic valve bag according to the invention in the state as in FIGURE 1.

FIGURES 14 and 15 show modified embodiments of the plastic valve bag according to FIGURE 13 in the same stage of manufacture.

FIGURE 16 is a section substantially along the line E-F of FIGURE 17 through a plastic valve bag according to FIGURE 13 in the next stage of manufacture.

FIGURE 17 shows the flat finished plastic valve bag according to FIGURE 13.

FIGURE 18 is a section along the line E-F of FIG- URE 17 with the bag walls slightly spread out.

FIGURE 19 shows the plastic valve bag according to FIGURES 13, 16, 17 and 18 in the filled, parallelepipedic state.

FIGURE 20 shows the filled plastic valve bag according to FIGURE 19 in a section G-H through the valve channel.

FIGURE 21 shows a known plastic valve bag in the filled parallelepipedic state in a section through the valve tube hanging down in a pear shape.

FIGURES 22 to 27 show the method of manufacture according to the invention in its various stages.

FIGURE 28 shows the opening of the gusseted tubular sections in a diagrammatic side view.

FIGURE 29 is a view in the direction of the arrow I of FIGURE 28 of the opened end of a gusseted tubular section.

FIGURE 30 shows the valve corner of an empty plastic valve bag with gussets according to a further embodiment.

FIGURE 31 shows the valve corner of the same bag when filled.

The construction of the first embodiment of the plastic valve bag according to the invention may best be understood if one considers a preliminary stage of its manufacture, as shown in FIGURES 1 to 6 in various embodiments. The bag according to the invention is made from opened by folding back of a piece 1 of the upper tube wall 1 about a folding line 9, thus forming a corner fold 6 and a gusset triangle 7. Beneath the corner fold 6 (see FIG. 2) there is then pushed a valve strip 10 whichis connected to the corner piece by a weld -11. The weld =1-1 projects beyond the side edges 12 and 13 of the valve strip 10 by pieces 14 for the sake .of safety. It is however also sufilcient if the weld 11 is as long as the valve strip 10 is wide. The width of the valve strip 10 should he at least so dimensioned that a Weld 15, 16 can be made along both its longitudinal edges 12 and 13 on either side of the gusset triangle 7 in order to join the valve strip 10 I to the folded back piece '1' of the bag side wall 1 and to the bag side Wall 2. The width of the tgusset triangle 7 determines the width of the top wall '17 of the parallelepiped (FIGURE 12) for-med when the bag is tilled,

which side comprises the side edges 85 and 86 running parallel with the valve channel and along which run the welds 15 and 16. The welds 15 and 16 are extended beyond the weld 11 and on this extension join the corner fold 6 to the bag top walls 1' and 2.

I According to the embodiment shown in FIGURE 3, the valve strip 18, which is otherwise identical with the valve strip10,is provided at its free end with fringeforming incisions 19 in order to enhance the sealing effect of the valve strip.

According to the embodiment shown in FIGURE 4, the valve strip consists of two individual strips .21 and 22 joined together by a weld 20, the strip 22 of which consists of a particularly thin plastic material, in order to increase the sealing action as a result of the great flexibility thereby produced. In addition the thinner strip 22 may also be provided with fringe-forming incisions.

In the embodiment according to FIGURE 5, the corner fold 23 is cut at right angles to its free edge at 24 and 25, in a manner known per se, whereby the free rectangular tips 26 and-27 extend the exposed portions of the bag Walls .1 and 2 correspondingly.

In the embodiment accordingly to FIGURE 6 the cuts 28 and 29 in the corner fold 30 are oblique, for example at the exposed portions of the bag walis- \l and 2 being extended by corresponding pointed tips 31 and 32, the purpose of which is indicated below.

After these preparations the folded back tube wall 1' is folded back again, thus commencing double folding of the valve strip 10, the corner fold and the gusset triangle 7, as shown in FIGURE 7, whereupon a complete flat folding is achieved as shown in FIGURES 8, 10 and 11, and the bag walls 1 and 2 are joined at both ends of the tubular section by a weld 33, 34, the gussets 3, 4 and 5, 8 being welded also within the welds 33 and 34 at the three corners 35, 36 and 37 which do not contain the filling valve forming part of this invention. After the welds 33 and 34 have formed the corners 35, 36 and 37 assume, when the bag is filled, a well known configuration of Welded plastic bags, as for instance illustrated in FIG. 23 of U.S. Patent No. 3,004,698.

In addition the gusset faces 6a may be joined to the adjacent bag wall 1, 2 respectively by diagonal welds 38 and 43, which'begin at the point of intersection of the gusset folds 44 and 45 with the welds 33 and 34 and lead at an angle 45 to the side edges 46, 47 and 48, 49. It should be noted that Whereas gusset faces 6a are merely extensions of the respective gussets 3, 4, 5, 8, the corner fold 6 extends transversely across the entire top wall width, taking thereby a trapezoidal shape when unfolded as illustrated in FIGS. .1, 3, 4, 1 3, :14, 15. The sides of the corner fold 6 are integral with the adjacent bag Walls \1', 2. At this stage the embodiment according to FIG- URE 5 gives a work-piece as shown in FIGURE 10 with edges 50, 51 running perpendicularly to the weld 33.

The embodiment according to FIGURE 6 gives at this stage a work-piece as shown in FIGURE 11, in which the edges 52, 53 run obliquely for example at 45, to the weld 33. After the introduction of the filling pipe into the valve opening 54 formed in the front part by the corner fold 6 and shown in FIGURE 9, the front point 55 (FIGURE 8) of the weld is subjected to very great stress. The embodiment according to FIGURE 8 without cuts in the corner foid offers least security against tearing of the weld 33 at this point 55, as can be seen particularly from FIGURE 12. It is therefore also proposedthat this part should be reinforcedby a cover strip 56 shown in dotted lines in FIGURE 12, which is preferably Welded on, leaving the corner fold 6 free. The cover strip 56 is made of strong plastic material and results in the case of the bag delivered in the flat state according to FIGURE 8 in the fact that the valve opening is easily opened, which is advantageous for gripping the bag in order to push it over the filiing connection, as .theworker can immediately get :under the strip 56 with his finger. Further, the cover strip 56 can also be made from a differently coloured plastic, as a result of which the valve corner is easily visible even at a distance.

The risk of tearing is met in another way by the cuts '24, 25 and 28, 29. As the point 57 shown in FIGURE 11 is flexible, tearing of the weld 33 at this point is practically impossible. A similar, though not such a marked effected can be obtained with the vertically running edges 50, 51 shown in FIGURE 10 giving a better appearance and avoiding the projecting corner 57 (FIGURE 11).

FIGURE 12 shows the para'llelepipe'd-ic bag formed after filling and particularly makes it clear thatthe valve strip 10 lies flat below the parallelepiped wall 17, so that the best possible valve action for sealing the bag contents from inside to outside and from outside to inside is given and bulging of the valve towards the outside is prevented. The valve strip 10 is fixed on both sides by the welds 15 and 16 and is stretched out parallel with the wall 17 flat beneath it. In the parallelepipedic state of the bag, the gusset triangle 7 together with the opened out gussets are located in the one side 58 formed by them. The diagonal welds 38 to 43 are likewise shown in FIGURE 12 as single or dotted lines only and are located, with gusset triangles partly bounded by them and forming themselves on assuming of the parallelepiped form in the sides 17 and 59.

The embodiment according to FIGURES 13 to 20 differs from the first embodiment in that as valve strip, a strip 60 is used, which is placed over the corner fold 6 and extended beyond the welds 15 and 16 as far as the edges 61 and 62 of the tube walls 1' and 2 and at least as far as the front edge 63 of the corner fold 6. On closing of the bag by the welds 33 land 34,,the valve strip 60 is welded within the weld 33 and forms moreover at the valve corner an extension 64 (FIGURE 17-. According to FIGURE 14 the valve strip 69 may again be provided between the welds 15 and 16 with fringe-forming incisions 19 and/or according to FIGURE 15 may consist of two strips 65 and 66 of different thickness.

According to a further inventive proposal, the valve insert of FIGS. 4 or 15 may consist of a unitary sheet of material that is thinner at one end than at the other, the said sheet of material having received a suitable crosssection with a thicker and a thinner part during extrusion. The entire width of the extruded length then corresponds to the desired valve strip length. A further proposal consists in rolling a length of material, extruded with uniform thickness and having the same width as the valve strip, intermittently at intervals corresponding to the length of the valve strip over a suitable part of the length, preferably under heat, and obtaining the valve strips by cross cuts after each rolled part has been welded to the valve strip. In the first proposal the valve strips are. obtained transversely with respect to the valve strip as i1- lustrated in FIG. 15, and in the second proposal longitudinally of the said valve strip.

As indicated in FIGURES 13, '17, 19 in dotted lines, the valve insert strip 60 may also be extended outwardly beyond the insert front edge 63 by a piece 67. After filling, the projecting end 67 can then be closed by a weld 68, so that a hermetically sealed valve is formed.

FIGURE 20 shows the cross section of the valve tube and indicates the extended course of the lower valve wall 60, 6 which is achieved through the welds 15 and 16. FIGURE 21 shows, in contrast to this, an embodiment, in which there are no welds 15 and 16. The inner end of the valve insert strip 60 hangs down in a pear shape from the weld 33 and does not assume a readily reliable closing position for the valve. The freely hanging valve is easily deformed and is inverted towards the outside by the contents. The welds 15 and 16 therefore constitute a substantial improvement of the valve as regards its effectiveness in closing the bag and retaining the desired closing form.

FIGURES l6 and 18 are easily understood without further explanation, as they constitute in the present embodiment the same states as do FIGURES 7 and 9 in the first embodiment.

In the present embodiment the gusset faces in the bag corners not containing the valve are preferably again joined to the bag walls by diagonal welds.

The manufacture according to the invention of the plastic valve bag according to the first embodiment is carried out as follows:

The gusseted tubular section according to FIGURE 22 open at both ends is folded up at one end in the corner to be formed into the valve, as shown in FIGURE 23, the corner fold 6 and the gusset triangle 7 being formed simultaneously with the folding back of the upper wall part 1 about the folding line 9 extending partly over the width of the workpiece. Then, as shown in FIGURE 24, the valve strip 10 is secured to the corner fold 6 by the weld 11, a heat-insulating intermediate layer preventing the simultaneous welding of layers lying underneath. Then the tube wall part 1 is folded back again, thus folding the valve strip 10, the corner fold 6 and the gusset triangle 7, resulting in the form shown in FIGURE 25. With interposition of a heat-insulating layer during the folding together, the welds and 16 are now produced on both tube walls with application of pressure and heat from above and below. The working steps described as shown in FIGURES 23, 24 and 25 are preferably carried out with the work-piece stationary. Between the carrying out of the various working steps, the workpieces are moved in the direction of the arrows 70, 71 from one working station to the next in the longitudinal direction of the tube. After carrying out the working steps according to FIGURE 25, the work-pieces are then moved transversely to their longitudinal direction in the direction of the arrow 72 to the next working station, because the heat-insul-ating layer interposed during folding together of the tube walls at the station of FIG. 25 does not then need to be swung out; instead the work-piece as it is moved in the direction of arrow 72 is stripped from the stationary heat-insulating layer. After reaching the working position according to FIGURE 26, the workpiece is moved in the direction of arrow 73 into the exact welding position and the weld 33 is produced. The workpiece is then moved in the direction of the arrow 74 into the next working position according to FIGURE 27 and is shifted in the direction of arrow 75 into the exact welding position for producing the weld 34. The plastic valve bag is thus substantially finished. The producing of the corner welding by the diagonal welds 38 to 43 then takes place, if necessary, in a further working position.

The preliminary opening of the forward end of the gusseted tubular section takes place, according to a further inventive proposal, directly after the separation of gusseted tubular sections from the underside of a stack of Work-pieces 76 (FIGURE 28). The stack 76 of workpieces supported in a known manner at the front and back by means of two angle ledges 77, 78, rests substantially on a roller 79 and supporting rolls of smaller diameter, not hown, arranged in front of and behind in its direction movement, which are so mounted and driven, that as they rotate below the stack they roll without friction alternately backwards and forwards being displaced simultaneously by the same amount. In the position 79' shown in dotted lines, the front end of the lowermost gusseted tubular section is gripped by means of suction openings 80 in the roller periphery and the workpiece is wound onto the roller as the later moves back and simultaneously rotates. On being withdrawn over the angle ledge 77, which might also be replaced by individual sprung angle pieces arranged at intervals next to one another, the lower tube wall 1 is the first to be pulled over the angular parts and is thus separated from the upper tube wall 2, the tube end thus being stripped open. Particularly at the gusset folds 44, 45 (FIGURE 29) the tube Walls 1 and 2 never actually adhere to one another, so that a progressive separation of both tube walls from one another can be obtained from these points. On reaching the lowest position of the suction openings 80, the tube wall 1 is still retained and the tube wall 2 hangs down to a considerable extent with the gussets opening, so that in this position grippers 82 secured to rotating chains 81, for example, can be pivoted into the open end of the tube, in order to grip the tube wall 2 now located at the bottom at its front edge and to take over further transport, after switching off of the suction air, of the tubular sections to the working positions illustrated in FIGURES 23 to 25. Raised fingers 83 arranged on the grippers 82 prevent falling down of the tube wall 1, so that the tubular sections reach the working station 23 with the front end already opened in order to be able to introduce the folding tools in a suitable manner.

In order to avoid tearing of the upper closing weld at its end nearest the valve, which is particularly subject to stress when the bag is filled, this end of the closing weld is, according to a further feature of the invention (see FIGURE 12) covered by a cover strip 56 welded at both sides of the weld. This cover strip offers the further advantage, that through the elasticity inherent therein, the valve opening of the bag delivered in the flat state can be opened more easily or automatically opens when a bag is withdrawn from a stack, so that the bag can easily be pushed onto a filling connection. The disadvantage of this construction has proved to be the welding on of a single cover strip, regardless of whether it is welded on the outer or inner surface of the part of the bag forming the base, because it may easily peel off in the case of undesirable impact with the filling connection when the empty bag is pushed on quickly.

The purpose of the invention is further to avoid with certainty the risk of peeling off of the cover strip.

This has been achieved according to the invention by the fact that the cover strip embraces with a bent back end the front edge of the bag walls connected 'by the closing weld and that the bent back end of the cover strip is welded to the bag walls at least at its longitudinal edges. This construction is shown in FIGURES 30 and 31. The plastic valve bag, of which only the valve corner is shown in the drawing, is made from a gusseted tubular section comprising the bag walls 1 and 2 and gussets inserted on both sides, of which only the one on one side has been shown and is designated 3, 4. By folding back the corner piece in the region of the gussets a corner fold 6 and a gusset triangle 7 are formed. Below the corner fold 6' is pushed a valve strip 10 which is connected thereto by a weld 11. The depth of the gussets which determines the width of the base of the filled bag, thus also determines substantially the width of the valve 7 strip 10 and hence the position of the weldsand 16 on both longitudinal edges of the valve strip projecting beyond the base width. The welds 15 and -16 are extended beyond the weld 11 and on this extension connect the corner fold 6 wit-h the bag walls 1 and 2.

The bag walls 1 and 2 are connected to one another at their upper end by a weld 33. vIn order to avoid tearing of the weld 33 at the end nearest the valve, this end is covered by a cover strip 85.

The cover srtip 85 is welded to the bag walls 1 and 2,

for example to the outer surface thereof, by means of welds 86, 87 on either side of the weld 33. With an end 88 bent back onto the inner surface, the cover strip encloses-the edge of the bag walls 1 and 2 joined to one another by the closing welds 33.

This bent back end of the cover strip is welded at its longitudinal edges to the bag walls 1, 2 by means of welds 89, 90.

In the embodiment described the bent back end 88 of the cover strip 85 is the longer end. It is however just as possible to make the bent back end the same length as or shorter than the end of the cover strip welded by means of the welds 86, 87.

What we claim is:

.1. A method for manufacturing plastic bags of the character described from open-ended tube sections having a pair of opposite gusseted side walls and a pair of opposite flat walls, comprising the steps of folding back a front corner of the upper wall of said pair of fiat walls, thereby forming a corner flap and a gusset triangle in one side wall of said pair of gusseted side walls, joining a valve strip to said corner flap by means of a welded seam, refolding said corner portion of the upper wall to its original position and simultaneously therewith folding said valve strip, said corner flap and said gusset triangle along their respective center lines, welding the two upright walls of the folded valve strip to opposite sides of said pair of flat walls along straight lines being parallel to the upper edges of said folded valve strip, and sealing said open ends of said tube section bymeans of a welded seam each.

2. A method as set forth in claim 1, wherein between the said steps of folding back a front corner of the upper wall of said pair of flat walls, joining said valve strip to said corner flap, refolding said corner portion of the upper wall to its original position and welding the two upright walls of said valve strip to opposite sides of said pair of flat walls, the said tube section is transported along its longitudinal axis, whereas between the last,

of the aforementioned steps and the said step of sealing said open ends of the tube section, it is transported transverse to its former movement, all said steps being effected while the tube section is stationary.

3. A method as set forth in claim 1, including a plurality of steps preceding said method, said plurality of steps comprising taking a tube section from overhead, stripping open the said pair of flat walls at one end of said tube section, turning said tube section in a substantially semicircular path, and allowing the lower wall of said pair of flat walls to hang down, thereby maintaining said pair of flat walls in a separated position.

4. The method as set forth in claim 3, including a plurality of steps preceding said method, said plurality of steps comprising storing a plurality of said bags in a stack, separating said pair of fiat walls by stripping said pair of walls open past spring biased stripping means and thereby causing the lower wall of said pair of walls to depend in spaced relationship from said upper wall and coupling the front end of the bag to be open and transporting said open bag along its longitudinal axis.

5. A method as set forth in claim 4, including a plurality of steps, subsequent to the steps set forth in claim 4 but preceding the steps of the method set forth in claim 3, of gripping said lower Wall of said open front of said bag by means of gripping mechanism, transporting said bag :along its longitudinal axis. by means of a transport mechanism, and maintaining said pair of flat walls in spaced relationship to each other by means of a separating mechanism during said transporting step.

References Cited by the Examiner UNITED STATES PATENTS 2,687,066 8/1954 Gilman 93-23 XR 2,968,432 1/1961 Craighead 22962.5 3,004,698 10/ 1961 Ashton 22962.5 3,087,670 4/ 1963 Rhodes 22962.5

BERNARD STIC KN EY, Primary Examiner; 

1. A METHOD FOR MANUFACTURING PLASTIC BAGS OF THE CHARACTER DESCRIBED FROM OPEN-ENDED TUBE SECTIONS HAVING A PAIR OF OPPOSITE GUSSETED SIDE WALLS AND A PAIR OF OPPOSITE FLAT WALLS, COMPRISING THE STEPS OF FOLDING BACK A FRONT CORNER OF THE UPPER WALL OF SAID PAIR OF FLAT WALLS, THEREBY FORMING A CORNER FLAP AND A GUSSET TRIANGLE IN ONE SIDE WALL OF SAID PAIR OF GUSSETED SIDE WALLS, JOINING A VALVE STRIP TO SAID CORNER FLAP BY MEANS OF A WELDED SEAM, REFOLDING SAID CORNER PORTION OF THE UPPER WALL TO ITS ORIGINAL POSITION AND SIMULTANEOUSLY THEREWITH FOLDING SAID VALVE STRIP, SAID CORNER FLAP AND SAID GUSSET TRIANGLE ALONG THEIR RESPECTIVE CENTER LINES, WELDING THE TWO UPRIGHT WALLS OF THE FOLDED VALVE STRIP TO OPPOSITE SIDES OF SAID PAIR OF FLAT WALLS ALONG STRAIGHT LINES BEING PARALLEL TO THE UPPER EDGES OF SAID FOLDED VALVE STRIP, AND SEALING SAID OPEN ENDS OF SAID TUBE SECTION BY MEANS OF A WELDED SEAM EACH. 